Uninvited guests can be a source of annoyance, and if you need to refer to them in a more polite way, there are a number of synonyms you can use. A common alternative is uninvited visitors, which suggests a more temporary presence rather than a permanent stay. Another option is unexpected guests, which may imply a more neutral tone. In a more formal setting, you might use the phrase unanticipated guests or unexpected visitors. If you're looking for a humorous way to refer to uninvited guests, you could consider using the term party crashers, which suggests a deliberate attempt to join in on an event.